At 240 V it interrupts 187 kA; at 415 V and 440 V it's rated 121 kA; at 500 V it drops to 76 kA. That SCCR range covers most industrial distribution panels fed from a medium-voltage transformer. It's a straight electromechanical breaker for main or feeder protection where you don't need adjustable trip curves or remote monitoring.
The 400 A rating holds up to 50 °C. Above that, it derates: 392 A at 55 °C, 384 A at 60 °C, 376 A at 65 °C, and 367 A at 70 °C. The breaker dissipates 77 W max, so panel cooling matters in a sealed box. That 138 mm width is wider than a standard 3-pole IEC MCB (typically 54 mm) — plan your DIN-rail or mounting-plate layout accordingly. Front protection is IP40, so it's fine for a closed panel; no washdown rating on the front face.